Dual colorimetric response of polydiacetylene/zinc oxide nanocomposites to low and high pH.

This contribution presents our continuation work on the color-transition behaviors of polydiacetylene(PDA)/ZnO nanocomposites prepared by using three types of monomers, 5,7-hexadecadiynoic acid (HDDA), 10,12-tricosadiynoic acid (TCDA) and 10,12-pentacosadiynoic acid (PCDA). The color-transition behaviors of these nanocomposites upon exposure to acid and base are investigated by utilizing UV/vis absorption spectroscopy. We have found that these PDA/ZnO nanocomposites exhibit colorimetric response at both low and high pH regions. The addition of acid causes the poly(HDDA)/ZnO, poly(TCDA)/ZnO and poly(PCDA)/ZnO nanocomposites to change color from blue to red at pH~5, 3.5 and 2, respectively. The color of pure PDA vesicles, on the other hand, is hardly affected at this pH range. At high pH region, the pure poly(TCDA) vesicles change color at pH~8 while it requires much higher pH to induce color transition of the PDA/ZnO nanocomposites. The mechanism responsible for color transition of the PDA/ZnO nanocomposites is explored by various techniques including infrared spectroscopy, zeta potential analyzer and light scattering. Our result provides a new approach for controlling the colorimetric response to pH of PDA-based materials.

Controlling the reversible thermochromism of polydiacetylene/zinc oxide nanocomposites by varying alkyl chain length.

In this work, polydiacetylene (PDA)/ZnO nanocomposites are successfully fabricated by using three types of monomers with different alkyl chain length, 5,7-hexadecadiynoic acid, 10,12-tricosadiynoic acid, and 10,12-pentacosadiynoic acid. The monomers dispersed in aqueous medium spontaneously assemble onto the surface of ZnO nanoparticles, promoted by strong interfacial interactions. The PDA/ZnO nanocomposites obtained via photopolymerization process are characterized by scanning electron microscopy, laser light scattering, infrared spectroscopy, and uv/vis absorption spectroscopy. The strength of interfacial interactions and morphologies of the nanocomposites are found to vary with alkyl chain length of the monomers. The PDA/ZnO nanocomposites also exhibit rather different thermochromic behaviors compared to their pure PDA counterparts. All nanocomposites show reversible blue/purple color transition upon multiple heating/cooling cycles, while the irreversible blue/red color transition is observed in the systems of pure PDAs. The shortening of alkyl side chain in PDA/ZnO nanocomposites leads to a systematic decrease in their color-transition temperatures. Colors of the nanocomposites at elevated temperature also vary with the alkyl chain length. Our results provide a simple route for controlling the reversible thermochromism of PDA-based materials, allowing their utilization in a wider range of applications.